Internal combustion engines are commonly used on mobile platforms, in remote areas or in lawn and garden tools. There are various types of internal combustion engines. Spark type engines compress volatile fuels, such as gasoline, before ignition. Compression type engines take in air and compress it to generate the heat necessary to ignite the fuel, such as diesel.
Although hydrocarbon fuels are the dominant energy resource for such engines, alcohols, especially methanol and ethanol, have also been used as fuels. For example, in the 1970s, gasohol, a blend of mostly gasoline with some ethanol, was introduced during the Arab oil embargo. Currently, the primary alcohol fuel is ethanol. In general, ethanol can be blended into gasoline in various quantities, normally at up to about 10%, which typically results in a higher octane rating than regular gasoline. Certain fuels being produced today primarily include alcohols, for example, E-85 fuel contains 85% ethanol and 15% gasoline, and M-85 has 85% methanol and 15% gasoline. There are, however, several drawbacks to the use of ethanol, such as energy deficiencies (ethanol provides about 39% less energy than gasoline), high blending RVP (at 10% of blending, RVP=11 psi), and incompatibility with existing transportation facilities.
Further limitations exist with respect to the use of grain-based fuels. For example, grain ethanol is expensive to produce. Producing sufficient quantities of grain ethanol to satisfy the transportation industry needs is not practical because food crops and feed crops are and have been diverted into grain ethanol fuel production. In addition, on a volumetric basis, both methanol and ethanol have relatively low energy contents when compared to gasoline. For example, methanol contains about 50,000 Btu/gal and ethanol contains about 76,000 Btu/gal, whereas gasoline contains about 113,000 Btu/gal.
Long chain alcohols can be used together with amines/anilines as inhibitors to prevent metal corrosion and rubber/plastics swellings caused by the ethanol fuels. These long chain alcohols, such as dodecanol, can also be used as emulsifying agents. Mixed low cost methanol and ethanol can be used with long chain alcohols to form alcohol blended diesels or used as emulsifying diesel adjustors. Long chain alcohols, however, are relatively expensive to produce. Methanol-based and ethanol-based diesels also suffer from the drawback that other additives are required to maintain a minimum Cetane number greater than 40 and to assure the diesel burns efficiently, such as long chain alcohols, alkyl esters and fatty acids.
Some time ago, lead was added to gasoline to boost its octane rating, thereby improving the antiknock properties of gasoline. Lead use, however, has being eliminated in most countries from gasoline for environmental reasons. In response to the need to phase out lead, gasoline sold in the United States and other countries was blended with up to 15% volumes of an oxygenate, such as methyl-tertiary-butyl-ether (MTBE), in an effort to raise the octane rating and to reduce environmentally harmful exhaust emissions. Due to its harmful effects, however, the industry is now replacing MTBE with the use of fermented grain ethanol, but as discussed above, producing the necessary quantities of grain ethanol to replace MTBE is problematic in specific regions.
Another additive that has been used in fuels is methylcyclopentadienyl manganese tricarbonyl (MMT). MMT has been a controversial gasoline additive for many years that is able to increase octane, but also increases emissions, which may have an adverse effect on health and exhaust catalytic conversion systems.
In lieu of these questionable additives having the various deficiencies described above, certain alcohols (e.g., butanols), and di-isobutenes (DIBs) can be used as combustible neat fuels, oxygenate fuel additives, or constituents in various types of fuels. When used as an oxygenate fuel, the BTU content of butanols and di-isobutenes is closer to the energy content of gasoline than many of the methanol or ethanol based fuels, as shown in Table I. HHV (second column) refers to Higher Heating Value, which is defined as the amount of heat released by combusting a specified quantity of the fuel at 25° C. and returning the temperature of the combustion product to 25° C., which takes the latent heat of vaporization of water in the combustion products.
TABLE IProperties of Butanols as compared to GasolineEnergyRVPDensity15%BlendBlendHydro-HHVRVPv/vRONMONd(RON −Den.carbon(MJ/kg)RONMON(R + M)/2(PSI)Blend(10%)(10%)MON)(g/cc)Gasoline45.589585907.57.59585100.747Alkylate429587922.62.699.196.130.7DIBs48.24101.185.793.41.71.712499.124.90.732-37.33115971060.834-512095250.808butanolt-butanol37.33115891020.444-510589160.7809MTBE37.961181021108.219118102160.74Ethanol29.85129102115.521511295170.79
Alcohols and DIBs can be prepared from olefins, or more specifically i-butene. Unfortunately, until now, there have not been any olefin hydration processes in place that are particularly effective for converting mixed olefins into alcohols, especially butenes into butanols, while simultaneously dimerizing the part of mixed olefins into oligomers such as DIBs.
Hydration reactions of butenes to butanols are commercially important as the products have several important industrial applications. Additionally, butanols have been deemed as a second generation fuel components after ethanol. These butanols can also be used as solvents or chemical intermediates for the production of corresponding ketones, esters, ethers, etc.
Butanols produced through typical bio-routes are not produced by efficient processes and are not produced in large enough quantity to meet the demanding needs of the butanol market. Hydration reactions, which are typically acid catalyzed, can be used, but it is costly. Because organic butenes have very low solubility in water, relatively strong acids are often required to achieve the desired kinetics to convert the butenes to alcohols. Other processes used to produce butanols are also expensive. For example, petrochemical routes to produce mixed butanols by hydroformation and hydrogenation from propylene and carbon monoxide can be extremely costly.
One conventional commercial method of production of secondary butyl alcohol includes using a two step processes in which the n-butenes are reacted with excess sulfuric acid (e.g., 80%) to form the corresponding sulfate, which is then hydrolysed to SBA, as follows:n-C4H8+H2SO4→2-C4H9OSO3H2-C4H9OSO3H+H2O→2-C4H9OH+H2SO4 During this process, the sulfuric acid becomes diluted to about 35% concentration by weight and must be re-concentrated before it can be reused in the process. One advantage of the process is a high conversion rate. Many other problems, however, are typically associated with the use of liquid catalysts. Among the problems includes the separation and recovery of the catalyst, corrosion of equipment and installations, and the formation of undesired byproducts, such as secondary butyl ether, isopropyl alcohol, C5-C8 hydrocarbons, and polymers. Some of these by-products complicate the purification of SBA.
Cationic exchange resins and zeolites are potentially important acid catalysts for olefin hydration and are known to offer substantial reaction rates in both polar and non-polar media. Attempts have been made to use sulfonated polystyrene resins that have been cross linked with divinyl benzene as catalysts for the hydration of olefins such as propylene or butene. These types of catalyst systems may offer several engineering benefits, such as ease in separation and provide a non-corrosive environment.
In spite of the currently available processes, there are currently no effective routes to producing mixed butanols and DIBs economically. Furthermore, conversion rates of olefin hydration are low at less than 10% per pass.
Thus, a need exists for processes and catalyst systems that allow for the simultaneous direct catalytic hydration and oligomerization of alkenes to alcohols and oligomers. It would also be beneficial if the processes and catalyst systems were both inexpensive and provided a route to industrially useful alcohols and a convenient synthetic route for the synthesis of alcohols in general.
Additionally, there is a need for a fuel additive or fuel that has an octane rating that is comparable to gasoline and having increased combustion efficiency. There is also a need for a fuel that reduces harmful emissions and airborne soot when combusted, either in neat form or as a fuel additive.
Finally, there is a need to provide a fuel or fuel composition having an octane rating and BTU value that is similar to gasoline, but wherein the fuel or fuel composition does not include the use of tetraethyl lead, MTBE, methanol, ethanol, or MMT. Additionally, it is desirable to provide a fuel additive that lowers the Reid Vapor Pressure of the fuel at least as well as, but without the use of, MTBE. It is also desirable that such fuels, fuel compositions, or additives include mixed alcohols that are produced from mixed olefin streams.